R/wb_sa.R

In titrationCurves: Acid/Base, Complexation, Redox, and Precipitation Titration Curves

#' Titration Curve for a Weak Base
#' 
#' This function calculates and plots the titration curve for a 
#' monoprotic weak base analyte using a monoprotic strong acid as 
#' the titrant. The calculation uses a single master equation
#' that finds the volume of titrant needed to achieve a fixed pH, 
#' as outlined in R. de Levie's \emph{Principles of Quantitative 
#' Chemical Analysis} (McGraw-Hill, 1997).
#' 
#' @param conc.base Molar concentration of the weak base analyte;
#' defaults to 0.10 M.
#' 
#' @param  conc.acid Molar concentration of the strong acid titrant;
#' defaults to 0.10 M.
#' 
#' @param pkw The pKw (or pKs) value for the solvent; defaults to water
#' as a solvent with a pKw of 14.
#' 
#' @param pka The pKa value for the weak base analyte's conjugate weak
#' acid; defaults to a pKa of 9, or a pKb of 5 for the weak base analyte.
#' 
#' @param vol.base Initial volume, in mL, of the solution that 
#' contains the weak base analyte; defaults to 50.00 mL.
#' 
#' @param plot Logical; if TRUE, plots the titration curve.
#' 
#' @param eqpt Logical; if TRUE, draws a vertical line at the titration
#' curve's equivalence point.
#' 
#' @param overlay Logical; if TRUE, adds the current titration curve
#' to the existing titration curve.
#' 
#' @param \dots Additional arguments to pass to \code{plot()} function.
#' 
#' @return A two-column data frame that contains the volume of titrant
#' in the first column and the solution's pH in the second column. Also
#' produces a plot of the titration curve with options to display the
#' equivalence point and to overlay titration curves.
#' 
#' @author David T. Harvey, DePauw University. \email{harvey@@depauw.edu}
#' 
#' @export
#' 
#' @importFrom graphics plot lines 
#' 
#' @examples
#' ### Simple titration curve with equivalence point
#' ex4 = wb_sa(eqpt = TRUE)
#' head(ex4)
#' 
#' ### Overlay titration curves using different pKa values
#' wb_sa(pka = 9, eqpt = TRUE)
#' wb_sa(pka = 7, overlay = TRUE)
#' wb_sa(pka = 5, overlay = TRUE)
#' 
#' ### Overlay titration curve for strong base and weak base
#' sb_sa(eqpt = TRUE)
#' wb_sa(overlay = TRUE)

wb_sa = function(conc.acid = 0.1, conc.base = 0.1, pka = 9, pkw = 14, 
                 vol.base = 50, plot = TRUE,
                 eqpt = FALSE, overlay = FALSE, ...) {
  veq = conc.base * vol.base/conc.acid
  ka = 10^-pka
  kw = 10^-pkw
  ph = seq(pkw, 1, -0.01)
  h = 10^-ph
  oh = kw/h
  delta = h - oh
  alpha = h/(ka + h)
  volume = vol.base * (conc.base * alpha + delta)/(conc.acid - delta)
  df = data.frame(volume, ph)
  df = df[df$volume > 0 & df$volume < 2 * veq, ]
  rownames(df) = 1:nrow(df)
  if (plot == TRUE) {
  if (overlay == FALSE) {
    plot(df$volume, df$ph, type = "l", lwd = 2,
         xlim = c(0, 1.5 * veq), ylim = c(0, pkw), 
         xlab = "volume of strong acid (mL)",
       ylab = "pH", xaxs = "i", yaxs = "i", ...)
  } else {
    lines(df$volume, df$ph, type = "l", lwd = 2, ...)
  }
  if (eqpt == TRUE) {
    x = c(veq, veq)
    y = c(0, pkw + 1)
    lines(x, y, type = "l", lty = 2, col = "red")
  }
  }
  invisible(df)
}